1. Field of the Invention
The present invention relates to an improvement in a valve-operating assembly of a driven rotation member and a cam, comprising a hub rotatably carried on a support shaft supported on an engine body, a cam formed on an outer periphery of one end of the hub, and a driven rotation member coupled to one end of the cam.
2. Description of the Related Art
A conventional valve-operating assembly of a driven rotation member and a cam is known as disclosed, for example, in Japanese Patent Application Laid-open No. 8-177416.
The conventional valve-operating assembly of the driven rotation member and the cam is entirely made of a metal, and hence has an increased weight due to the driven rotation member of a relatively large diameter, thereby hindering the reduction in weight of an engine to some extent.
Accordingly, it is an object of the present invention to provide a valve-operating assembly of a driven rotation member and a cam, which is lightweight and moreover, is excellent in lubrication of the cam and hub.
To achieve the above object, according to a first feature of the present invention, there is provided a valve-operating assembly of a driven rotation member and a cam, comprising a hub rotatably carried on a support shaft supported on an engine body, a cam formed on an outer periphery of one end of the hub, and a driven rotation member coupled to one end of the cam, wherein the cam and the hub are integrally formed of a sintered alloy; wherein the cam has a recess defined in one end face thereof; and wherein the driven rotation member is made of a synthetic resin and mold-coupled to the cam and the hub so that the recess is filled with the synthetic resin of the driven rotation member and an outer periphery of the hub is wrapped with the synthetic resin. The driven rotation member corresponds to a driven pulley 25 in an embodiment of the present invention, which will be described hereinafter.
With the first feature, the driven rotation member is made of the synthetic resin and hence, is relatively lightweight in spite of its relatively large diameter. This can contribute to a reduction in weight of the assembly of the driven rotation member and the cam, and in turn to a reduction in weight of an engine.
Moreover, since the driven rotation member is mold-coupled to the cam and hub, a special securing means is not required, leading to a further reduction in weight of the assembly.
Further, since the recess is filled with a material of the driven rotation member made and an outer periphery of the hub is wrapped with the material upon mold-coupling of the driven rotation member to the cam and the hub, coupling forces of the driven rotation member to the cam and hub in rotational and axial directions can be increased.
According to a second feature of the present invention, in addition to the first feature, the recess is formed so that the shape of its inner surface substantially corresponds to that of an outer peripheral surface of the cam.
With the second feature, the recess is of the shape substantially corresponding to the outer peripheral surface of the cam and hence, the coupling force of the driven rotation member to the cam, particularly in the rotational direction, can be increased effectively. Moreover, the wall thickness of the cam around the recess is substantially uniform, and hence the thermal deformation during sintering of the cam can be suppressed to contribute to an enhancement in accuracy of a cam profile.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.